Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
  • G01V15/00—Tags attached to, or associated with, an object, in order to enable detection of the object
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/07—Endoradiosondes
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B90/00—Instruments, implements or accessories specially adapted for surgery or diagnosis and not covered by any of the groups A61B1/00 - A61B50/00, e.g. for luxation treatment or for protecting wound edges
  • A61B90/90—Identification means for patients or instruments, e.g. tags
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B90/00—Instruments, implements or accessories specially adapted for surgery or diagnosis and not covered by any of the groups A61B1/00 - A61B50/00, e.g. for luxation treatment or for protecting wound edges
  • A61B90/90—Identification means for patients or instruments, e.g. tags
  • A61B90/98—Identification means for patients or instruments, e.g. tags using electromagnetic means, e.g. transponders
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
  • A61F13/00—Bandages or dressings; Absorbent pads
  • A61F13/15—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators
  • A61F13/44—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators with radio-opaque material or signalling means for residual material
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B34/00—Computer-aided surgery; Manipulators or robots specially adapted for use in surgery
  • A61B34/20—Surgical navigation systems; Devices for tracking or guiding surgical instruments, e.g. for frameless stereotaxis
  • A61B2034/2046—Tracking techniques
  • A61B2034/2051—Electromagnetic tracking systems
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B34/00—Computer-aided surgery; Manipulators or robots specially adapted for use in surgery
  • A61B34/20—Surgical navigation systems; Devices for tracking or guiding surgical instruments, e.g. for frameless stereotaxis

Definitions

• This invention relates to the detection of tagged objects and devices and, particularly, objects and devices utilized in body cavities during surgery.
• Surgically acceptable procedures for detecting and removing foreign objects include counting the objects used in the operation.
• X-ray detection is also used to locate foreign objects. It is not uncommon, however, for object counts to be incorrect. Furthermore, even x-ray detection is not flawless.
• objects such as surgical sponges, are typically embedded with an x-ray opaque material to make them more readily detectable, surgical sponges are often crushed into very small areas within a flesh cavity, whereby x-rays are not always able to sufficiently highlight them for detection.
• an x- ray is a time delayed detection method because of the requirement for film development (even with quick developing films).
• a patient will often be completely sutured closed before x-ray results are obtained, which may indicate the location of a foreign object within the patient.
• the detection delay may, therefore, result in the surgical team re-opening the patient, thereby increasing the morbidity of the operation.
• Surgical objects such as sponges should be deformable to conform to body cavity work area. If the tags are shrunk and encapsulated so that they would take up a sufficiently small deformation resistant area within a sponge, they could be used without impeding the function of the sponge. However, as the area of the described tags is shrunk, their coupling will decrease, making them almost invisible to a typical detection system contemplated for use in surgery.
• the present invention features a method and apparatus for detection of objects such as surgical sponges, which have remained in a patient after surgery.
• An apparatus of the invention comprises detection tags which are sufficiently small that they do not impede use of an object such a surgical sponge, or are larger but flexible, are reliable in discriminating detection, irrespective of the tags orientation, and are economical for widespread use in objects such as garments.
• the present invention also provides an apparatus and method/system for detecting tags that are sufficiently small for placement in a surgical apparatus.
• the present invention comprises a method and apparatus for the detection of objects including foreign objects not intended to remain in a body cavity during or after surgery.
• the invention uses detection tags that do not adversely affect use of surgical apparatus and an interrogation and detection device providing reliable and strong detection signals.
• An apparatus for the detection of an object contained in a work area includes a tag element affixed to a larger-sized object containing an electronic signal emitter within the protective means.
• the apparatus which works well even with low Q tag elements, further includes an operable interrogation and detection member (or scanning/wand detection device), enabled to locate the tag element which is within a predetermined distance therefrom.
• the interrogation/detection member includes (i) first means for the emission of pulsed wideband signals in each coordinate direction, each wideband signal including a signal which prompts the tag element to provide a return signal, and (ii) second means for the reception and analysis of the return signal.
• the apparatus operates such that multiple pulsed signals emitted from the first means cause the return signals from the tag element to increase in the intensity at a detectable frequency sufficiently over ambient noise levels to facilitate detection of the tag element and object attached thereto.
• the interrogation and detection member contains an antenna portion shared for both transmit and receive functions and a handheld portion to which the antenna is detachably connected, the handheld portion contains the electronic transmitting/receiving components and the antenna portion includes a single or a plural ring-shaped antenna, the latter emitting a pulsed wideband signal as an electromagnetic signal in each coordinate direction of the multi-directional coordinate system employed.
• a method for the detection of one or more objects in a work area such as in a surgical site including (i) attachably providing each foreign object with a much smaller element which does not interfere with utilization of the foreign object, the tag element, which may be a low Q tag element, including means for responding to a wideband signal from a scanning detection device and returning a response signal centered about a specific but not a predetermined frequency.
• the method calls for scanning the surgical site with a scanning detection device containing a transmitter and receiver, the transmitter emitting either one of a pulse-width modulated wideband interrogation signal or a voltage-modulated wideband interrogation signal, the wideband interrogation signal containing a frequency at which the tag element responds with a signal response signal for each emitted pulse reaching the tag element, each pulse of the wideband interrogation signal being of such duration as to cause the return signals from the tag element to become cumulatively increased in intensity, resulting in a narrow band return signal having sufficient intensity to be distinguishable from background noise, to facilitate detection of the tag element and object attached thereto.
• FIG. 1 is an exploded view of a bead type tag used in the present invention
• FIG. 2 is a cross section view of a thread type tag used in a second embodiment of the present invention.
• FIG. 3A depicts a typical configuration for the hand held detector of the present invention
• FIG. 3B depicts a second configuration for the hand held detector of the present invention
• FIG. 4 depicts a thread for weaving into a surgical sponge having multiple beads of the type shown in FIG. 1 ;
• FIG. 5 depicts a manner in which the tag bead of FIG. 1 is attached to a laparotomy sponge with a rivet attachment;
• FIG. 6A is a block diagram of the electronics utilized in the detector of FIG. 3;
• FIG. 6B is a block diagram of another embodiment of the electronics utilized in the detector of FIG. 3;
• FIGS. 7A and 7B are graphical depictions of the wideband transmitter signal and the narrow return signal of the tag as differentiated from background noise, respectfully, and FIG. 7C is an explanatory illustration depicting transmitter energy decay between a wideband pulse excitation system and a traditional narrow band sinusoidal (high Q) excitation system and how they affect detection of the return signal from the tag.
• FIG. 8 is a side view of another tag embodiment having three orthogonal tank windings to ensure detector wand cutting of a field line regardless of tag orientation and manner of wand deployment; and
• FIGS. 9A and 9B depict detector wand deployment relative to a tag and various possible tag orientations with respect to marked field lines.
• a scanner comprises an electronic signal emitting detection device in the configuration of a movable wand with an interrogation ring (i.e., emitting antenna), and one or more tag elements (for each object to be detected) with each tag being of a size which is sufficiently small as not to impede the function of deformable objects such as surgical sponges to which the tags are affixed.
• the tag is no greater than about 12 mm in its largest dimension.
• the tag element is electrically insulatively encapsulated in a bio-inert (if used in a surgical environment) hard plastic or glass in the form of a bead.
• the tag is contained within a electrically insulative bio-inert flexible thread element (preferably elastic) which is attached to the object to be detected.
• the flexible, i.e., deformable, thread may be, for example, in about 3" in length.
• the bead may be directly heat sealed to the threads of the sponge, adhered with a medically acceptable adhesive, or may be provided with an attaching thread for attachment thereto. Tags already in a thread configuration are directly woven into the sponge material where conditions of size are less stringent.
• the tag comprises components that provide a return signal in response to the signal emitted from the detection device.
• the tags generally, have a single signal emitting element such as an encapsulated miniature ferrite rod with wire winding, coupled with a capacitive means such as a capacitor for use in a bead embodiment, or a simple single loop wire, with winding, contained within an elastomeric coating as a thread element.
• An optional diode may be utilized to protect against tag-burn-out where an electric arc-weld type device known as a bovie, with applied electrical current, is used as a scalpel proximate thereto.
• the number of wire windings may be reduced to reduce any burn-out effect.
• the tag emits a small response signal, of general but not specifically known frequency, which would normally not be readily detectable because of its weak strength and non-predetermined nature.
• the signal emitting detection device in this embodiment utilizes pulsed signal emitting means with wideband capability, covering a signal range including that of the tag's response signal.
• the pulsed signals trigger a continuing response signal from the tag in its response frequency range which increases in intensity to the point where it becomes differentiable from background noise and is detected within the wideband range by the signal detector as an indication of the presence of the tag. Since the precise frequency of the signal response is not necessary or even pre-determined, expenses in electronics for emission and detection are typically reduced.
• the immediate turn off of the signal during pulses permits the quick location of the tag return signal (typically on the order of microseconds from transmitter turn-off), so that even a low Q tag may be utilized.
• Tag characteristics in various embodiments include ruggedness, whereby the tag should be able to withstand high temperatures, and pressure from surgical instruments, (i.e. clamps) as well as all liquid immersions, bovie emissions, and high voltage cardiac defibrillation.
• the tags should be crush proof and the bead tags should be non-deformable under surgical use.
• Bio-inert plastics, such as are used with prosthetics, as well as bio-inert glass are useful for the encapsulation protection of the radiating elements.
• the tags are detectable from a distance of at least about 12 to
• the detector device is adapted to be handheld and thus lightweight, and wand-like in configuration. This obviates the need for special bed installation or room adaptations, with detection equipment, as utilized in some prior art embodiments.
• the detector of the present invention is accordingly portable and movable with the patient.
• the detector device is provided with a radarlike system coupled with passive magnetic technology.
• the system for detecting surgical devices is defined by two basic elements:
• a detection wand-the hand held unit which the surgeon or surgical staff member can use such as within approximately 12 to 18 inches of proximity to the patient and the surgical site, for verification of object removal; with the head of the device, being a single ring-shaped antenna or a plural ring-shaped antenna, which can be sterilized and replaceable, for open wound intrusion; with the wand containing transmission and receiving signal means; and
• the detection system uses a ring back technique (which excites a tag element, previously placed on a medical instrument or on/in a surgical sponge), by radiating magnetically coupled energy to the tag, through the loops of the antenna.
• a ring back technique which excites a tag element, previously placed on a medical instrument or on/in a surgical sponge
• the use of magnetic coupling is particularly preferred since magnetic coupling is almost inert to tissue and water immersion, conditions most prevalent in a surgical environment.
• the transmit cycle from the detection wand utilizes a pulsed method to excite the tag(s) with signals over a fairly widebandwidth wherein sinusoidal components of the resonant tags exist in the pulses.
• This permits the use of economical tag components since center frequency is not required to be at close tolerances.
• the pulsed transmissions allow the system to pump more energy into the tag through several pulses, before ring back occurs, with extending ring back duration, thereby effectively increasing the range of detection to usable levels.
• the tag when excited, transmits an image signal of its resonance decay, via magnetic coupling, back to the detection wand which contains a receiver circuit.
• the detection wand has a single loop antenna structure shared for both transmit and receive functions, with one loop for transmit and receive, through which the image of the numerous tag return signals (in response to the pulse signals) are processed, to create better signal to noise performance.
• the signal transmitter therein is multi-turn single loop, wherein band of operation frequency is lowered by reducing operational inductance of wire or by shrinking the diameter of the loop.
• Return signal averaging is used to "see” the signals (as a single enhanced signal) through noise. This "visibility" condition is a result of the multiple signals being added to each other directly whereas noise tends to add at its square root, thereby resulting in an enhanced single narrowband signal rising from the background noise levels.
• the detection wand contains a multi-loop (multi-ring) antenna, for example, it may be structured with three (3) loop antennas arranged as three (3) mutually orthogonal rings, for both transmit and receive functions.
• a multi-loop (multi-ring) antenna for example, it may be structured with three (3) loop antennas arranged as three (3) mutually orthogonal rings, for both transmit and receive functions.
• Signal processing technique allows the system to characterize a tag via its ring back response, and return (response) signals which are not indicative of tags are easily discarded by comparison to the characterized signature map. This provides detection results which are far superior to traditional ring-back systems which rely on either resonance or center frequency detection based on phase shift around a center frequency.
• Q which refers to the quality factor, relates to, for example, the energy transfer between tag and detector in an RFID electromagnetic system. Function is not dependent alone on the Q of the tag but on the energy transfer between the tag and detector at a given distance and coupling (or at an energy level and effective area of cross section between a tag and detector).
• the present invention will function well under lower Q operation characteristics than that typified by a narrow band (traditional RFID) approach, because the method of excitation and ring back are managed differently.
• the apparatus and method/system of the present invention features an interrogation/detection scheme, which can use wideband methodologies.
• the pulse generator is set to emit pulses to excite a range of frequency components.
• the pulses are controlled for duration and interval to maximize energy transfer to the tag over a desired bandwidth.
• the pulses are sent through a driver and amplified to an appropriate signal level and a transmit amplifier is designed to shut off quickly.
• an untuned transmitter is utilized, which relies on the pulse method to insure energy transfer to the resonant tag.
• the receiver is also wideband whereby it can see tags over a wide spectrum benefiting from fast transmitter signal decay.
• the receiver further comprises limiters to insure that the transmit cycle does not saturate it.
• DSP Digital Signal Processing
• the time when a signal is sampled is controlled from a TX inhibit clock and control logic in order to insure that a signal captured is at the appropriate time from the transmitter shut off time.
• Signal processing such as averaging is applied either in through clocking with the sample and hold or summing circuit or by a microprocessor ( ⁇ P) or a DSP.
• ⁇ P microprocessor
• the averaging technique is similar to a synchronous detector creating a super narrow digital like band pass function (increasing signal to noise of tag return signal).
• a microprocessor If a microprocessor is used, it can then store the output of an analog to digital converter. In addition, the microprocessor may be used to characterize ring signature. Depending on the level of complexity of signal processing which may be necessary, the DSP may not be needed or may be external.
• the transmitter In normal operation the transmitter, while it is exciting the tag, is blocking any possible return signal from the tag. That is the system is, in effect, half duplex. Accordingly, one problem encountered in design of a detection wand is reducing the turn off time of the transmitter signal.
• the tag When the transmitter is on, the tag will be excited and will also radiate a return signal. At the time the transmitter is turned off, the tag is at its peak amplitude of a radiated signal. But the transient transmitter signal is still present, so the tag signal will not be easily visible until some time later.
• the transient signal from the transmitter is from capacitive and inductive components in the transmitter/receiver circuitry and exists even if the transmitter is shunted at turn off. Accordingly, the transmitter/receiver circuit of the present invention is made wideband using low loop capacitance in the analog front end. Thus, greatly improved distance or sensitivity are achievable with small low cost tags having weak signal return.
• the present invention uses the same excitation frequency component to power the tag and to receive ring back from the tag while being wideband in design, and the combination of wideband design coupled with signal processing technique allows for enhanced performance of range, and reduced tag cost and tag size.
• the present invention permits the tags to remain attached to the sponge or instrument to be located. Accordingly, the present invention encompasses many ways for the detachable resistant attachment of the tag to the sponge or instrument. Because of the more severe use (i.e., deformation), involved in sponge use, good attachment thereto is most problematic.
• the tags of the present invention in one embodiment are made into a hard object to resist deformation, and each is coated with an insulative, bio- friendly and inert shell and, according to one example of a preferred embodiments, is made of a ferrite core with some loop wire and a capacitor (optionally with a diode for burn-out protection) contained, for example, within a 5 mm-12 mm oval shape plastic shell, although not limited thereto.
• a string is integrated into the encapsulating shell to accommodate the tag to be integrated in the cloth manufacturing procedure used in manufacturing the sponge.
• a rivet button cell is attached to a corner of the sponge material. For a lap pad, the button cell may be added to the lap pad drape loop extension.
• the tags can be adhered to the substrate to be detected by materials such as surgical adhesive implaniable FDA USP class VI.
• the detector and tag provide positive signal evidence (audio or visual, e.g., at sufficient signal strength, an LED signal lights up) that a sponge or similar object remains in a body cavity (or that an object is located within a scanable area).
• positive signal evidence audio or visual, e.g., at sufficient signal strength, an LED signal lights up
• exact location is not as desirable and is often not as necessary, since mere knowledge of the presence of a sponge is sufficient for a surgical team to quickly manually locate the object within a body cavity (i.e., in the location where sponges were actually used). It may however, be desirable to actually locate the object or at least narrow the range of the site in which the object may be located. Accordingly, detectors of different ranges may be utilized, once the presence of an object has been determined.
• detectors may be modified in antenna (or loop) dimension or in power used for signal emissions. With regard to the latter, a single detector can be used, e.g., one with variable power output (the level of which is controlled in stages with successively narrowed ranges) to locate the "lost" object with greater precision.
• a fixed repetition rate of putting out pulse sequences to excite tags may be susceptible to continuous wave noise (i.e., signals close to the tag frequency). Accordingly, in a further embodiment, the pulse signal frequency is varied in random fashion to make it very difficult for continuous wave noise to affect the system, since it will become very out of phase with the tag resonance. This is similar to a spread spectrum approach in frequency hopping.
• broad band noise such as is generated with lightning or use of a bovie, is not treated as an adding sample of pulse signal return by tag and is excluded by sampling and shunting to ground.
• the tags may be initially configured with three orthogonal tank windings. These comprise horizontal and vertical tank circuits in addition to the center tank circuits described for use with the tags. With these additional tank circuits, there is always a loop coil on the tag which will have field lines from the detector wand cutting or passing therethrough. This avoids any misreadings caused by simple placement of the detector wand on the site, instead of with a lateral waving motion.
• the geometry of the tag may be varied, such as to enhance its reproducibility, and the various tag shapes may include cubic, cylindrical, spherical, etc.
• FIG. 1 an example first embodiment of a tag (tag element) 1 in the form of an oval bead, with dimensions of about 10 mm length and 2 mm diameter, although not limited thereto, is shown with encapsulated miniature ferrite rod 2 with coil 2a and capacitor 2b.
• a protective shell such as the hard bio-inert plastic 3 encapsulates the coil, rod and capacitor to protect it from damage from pressure and body fluids.
• Elastomeric, x-ray opaque bonding strings 4 serve as a means by which the bead is attached to a surgical sponge. Because of its very small dimensions, the bead does not impede deformation of the sponge to which it is attached.
• Diode 5 shown in dotted line outline, is optionally included as electrical protection against electrical burnout from proximate electronic instruments.
• the time constant of the tag may be selected to avoid introducing an unacceptable delay between the transmission of the interrogation signal and the return signal from the tag.
• an example second embodiment shows a tag 1' in the form of a thread with single loop wire 2a' (shown as an elongated U-shaped wire)with capacitor 2b' enclosed within an elastomeric coating or sleeve 3'.
• the diameter of such tag is similar to that of the bead embodiment of about 2 mm but because of its high flexibility, its length can be greater, e.g., including to about 3" (about 75 mm) and it provides its own thread-like attachment means.
• the bead 1 tag element of FIG. 1 and the thread (or cord type tag element) 1' of FIG. 2 are detected by a wand (scanning) detection device such as interrogation/detection device 10, shown in FIG. 3A, which comprises handle 11 (with contained electronics, e.g., as schematically set forth in the block diagram of FIG. 6A or FIG. 6A with 6B, including, with power supply source of battery or transformer and standard AC electrical connection), although not limited thereto.
• Interrogation and receiving ring 12 of the device 10 is an antenna ring with a nominal diameter of between 8-12", although not limited thereto. Since the ring 12 is in proximity to the surgical site for detection, it is sterile and removable for sterilization or replacement. It may also be replaced with, for example, a smaller diameter ring for more precise location once it has been determined that a "lost" object is present.
• the interrogation and receiving ring 12 functions to transmit an electromagnetic signal to the tag 11 and to receive a response signal from the tag 1.
• the size and geometry of the ring 12 are, in practice, chosen such that the ring 12 is capable of receiving the response signal from the tag 1. For instance, where the ring 12 is too small, the ring 12 may, upon a sweep of a patient's body, miss detecting the tag 1. Reducing the size of the ring 12 beyond a certain point also limits the distance from the patient's body at which the interrogation/ detection device 10 can detect the tag 1.
• the ring 12 may be a solenoidal coil.
• the device 10 in an example alternative embodiment of an interrogation and detection device (or wand detection device or scanning detection device) of an apparatus and method therefor for detecting an object, to improve the ability of the device 10 to detect the response signal from the tag 1 , the device 10 includes three rings 13, 14, and 15.
• the three rings are, in this example embodiment, mutually orthogonal to one another. Rings 13, 14, and 15 transmit the electromagnetic signal to the tag 1 in the x, y, and z-directions, respectively.
• the three orthogonal rings may be embedded (contained) in a housing.
• This embodiment is useful in that a tag, oriented to receive an electromagnetic signal in only one of the x, y, or z-directions, is assured of receiving the emitted signal and, as such, transmitting a response signal (i.e., a return signal) to the device 10.
• a response signal i.e., a return signal
• Two modes of operation are possible, simultaneous or round-robin transmit excitation.
• the round robin mode provides best receiver sensitivity given directionality of energy over time.
• the three rings 13, 14, and 15 transmit in succession, such that only one of the three rings 13, 14, and 15 is transmitting at any one time. Following a transmission by one of the rings 13, 14, and 15, there is a brief intermittent period before transmission by another of the rings 13, 14, and 15 is effected. During this intermittent period, the rings 13, 14, and 15 are used to determine whether a response signal is forthcoming from the tag 1. The intermittent period is, however, on a very small order of time, such that the tag 1 , even where it changes its orientation, will receive the electromagnetic signal and, consequently, send a response signal to the device 10, allowing the tag 1 to be detected.
• the round-robin method requires that the clocking between transmit cycles and the inhibit cycles of each ring be coordinated properly to avoid overlap to the prior excitation and receive period of the last used ring.
• the three orthogonal rings provide receiver signal information in three planes.
• the receiver information is aggregated into a threshold measurement for tag(s) presence.
• the receiver circuitry could have three receivers and provide signal information in three planes creating a digitization or special location information.
• a thread 6 with multiple beads 1 may be bonded, stitched or woven into the fabric of surgical sponge 8, as a low cost detection tag with increased signal strength.
• tag 100 is provided with a rivet attachment member 101 and eyelet 102 whereby the tag is attached to a laparotomy sponge 103 which is typically provided with standard marker loops 104.
• the electronics for both interrogation and reception of return signal are contained within the device 10.
• the device 10 contains a pulse generator 30 with a base clock 30a and rep. clock 30b, as well as transmitting driver 31 and tx (transmitter) amplifier 32 as the signal goes to antenna loop or ring 12.
• the loop ring 12 receives the signals from any of the tags which may be present within the interrogation range thereof (e.
• RAM random access memory
• ⁇ P microprocessor
• ROM read only memory
• DSP digital signal processor
• the return signal 71 shown in FIG. 7B, which commences with the shut off of the transmit signal 70 (see FIG. 7A), rises in intensity (e.g., magnitude) to a level easily distinguishable from the background noise 72 as the detector nears the tag thereby facilitating detection of the location of the surgical sponge (or other object) attached to the tag, for example, by triggering an audio and/or visual alarm.
• intensity e.g., magnitude
• the tag element is excited using a low Q wideband transmitter.
• this may be considered a less efficient forward energy transfer approach, it does have the ability to clamp the transfer decay rapidly and allow the tag signal to be seen earlier in its return decay.
• a digital ⁇ P embodiment may be used to implement most of the component parts of the above implementation in software and mixed signal chip technology. It is well known (digital signal processing) to a skilled digital design engineer to apply, for example, a single chip ⁇ P or DSP (digital signal processing) parts to handle clocking, filtering, digital amplification, threshold detection, phase detection, digital pulse generation and many other signal- processing functions to make the aforementioned transmit and receive system. Also, numerous combinations of known filtering schemes can be applied to achieve improved signal discrimination. In general the application of digital signal processing techniques with RFID (Radio Frequency Identification) have in the past been less important because the transmit/receive systems employed narrow bandwidth operation schemes using highly tuned, high Q embodiments.
• RFID Radio Frequency Identification
• the pulse generator 30 is chosen to generate a series of pulses centered about 0V. In other words, the pulse generator 30 generates a series of pulses having a DC value of 0V. In such a manner, equal amounts of positive and negative energy are transferred to a proximate metal object. As such, the eddy currents created in the proximate metal object are minimized or eliminated, such that the device 10 is prevented from coupling to loop transients in the proximate metal object.
• the pulse generator 30 may be implemented to generate such pulses using, for example, a balanced bipolar driver circuit.
• the pulse generator 30 is implemented in such a fashion as to modulate the transmitted pulses.
• multiple drive voltage levels are used.
• the voltage levels of the pulses are varied over time.
• the transmit driver 31 in FIG. 6A is controlled by the pulse generator (likely implemented as software/firmware routine in ⁇ P or DSP), and can switch or modulate a variety of drive voltages. Not shown are the voltage sources, and modulation elements, as these should be well established for one familiar in circuit design art.
• pulse width modulation (PWM) and repetition management are first employed to shape the drive waveform.
• the pulse generator 30 in FIG. 6A which, for example, may be implemented using firmware in ⁇ P or DSP, alters pulse width and number of digital signals applied to the transmit driver by turning them on or off creating pulse management. Modulation either via multiple drive voltages or pulse width variation can also help to discriminate tag signals from noise sources, as a response to modulation by the tags will produce different spectral behavior than other noise sources. This is especially valuable in an implementation with a DSP where signal processing using, for example, FFT (Fast Fourier Transforms) might be used to validate a tags signature in the frequency domain. Signal processing techniques such as using FFT are well established with regard to radar systems and should be available to one familiar with DSP based digital design technology.
• FFT Fast Fourier Transforms
• the pulse generator [00072] To further increase the signal to noise ratio, the pulse generator
• the pulse generator 30 is, in another embodiment, implemented as a spread spectrum driver. That is, the repetition rates of the transmit drive pulses are varied in a more random manner over time or are made less periodic. Such implementation can be effected through using DSP to create random synchronous excitation, a technique well described to those familiar with signal processing in wideband systems.
• the pulse generator 30 By implementing the pulse generator 30 as such, the device 10 is made much less sensitive to constant frequency sources that may be within approximately 5% of the resonant frequency of the tag 1. To implement the pulse generator 30 as such, the time interval between successive drive pulses is altered. Since the phase detection, as discussed below, is slaved to the drive timing, operation of the device 10 will not be adversely affected.
• the relative phase of external signals will change from pulse to pulse and will thus be averaged out in the phase detector.
• the drive timing is changed by one-half cycle of the tag frequency with each drive pulse.
• the resulting spectrum is complex enough that it is not likely to be matched by other kinds of transmissions in this band.
• the received signal from the tag 1 may be passed through an initial filter 300, preamplifier 301 , a DC Filter 302, and a second preamplifier 303.
• a critically damped second or third order filter such as, for example, a Bessel low pass filter 304 may be provided, also, at the input to a phase detector 305 along with detector 305.
• the phase detector 305 may be implemented in a variety of manners.
• the phase detector 305 uses the transmitted pulsed waveform to locate the response signal received from the tag 1. For example, when the pulse generator 30 generates a pulse, the phase detector is turned off. When, on the other hand, the pulse generator 30 is not outputting a pulse, the phase detector is turned on. In such a fashion, the phase detector is better equipped to locate the response signal from the tag 1.
• the phase detector 305 could be modified to specifically reject the recovery tail from the transmitter, although this may not be necessary since the shaping of the pulsed waveform, as described above, will tend to accomplish the same thing.
• the output of the phase detector is integrated via S/H and/or A/D converter 41' to produce a threshold signal for triggering the alarm, indicating the presence of a tag or tags.
• the signal is compared for width, pulse shape, or match to a much more articulate set of image criteria (not just integration level), thus improving the rejection of false signals and providing more sensitivity potential to alarm outputs.
• a tag 200 which is detectable regardless of orientation is provided with three orthogonal tank circuits 201a, 201b and 201c, respectively shown as horizontal and vertical in addition to the center tank circuit previously described.
• a single capacitance element 202 is utilized in addition to the ferrite core 203.
• deployment of detection wand 10 detects magnetic field lines regardless of tag orientation.

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